The goal of this study is to determine the role of pulmonary metabolism of essential fatty acids, e.g., arachidonic acid in the etiology of intra-arterial thrombosis. This study will determine the factors controlling production of prostaglandins and thromboxanes by pulmonary tissue and vascular endothelium. Using in vitro systems, we have studied the role of peroxidase in control of PGI2 biosynthesis. Chemicals that stimulate the peroxidase reduce level of hydroperoxides that inhibit PGI2 biosynthesis, resulting in a stimulation of PGI2 production. In the future, we intend to study the role of prostaglandin peroxidase in controlling both hydroperoxy fatty acid and possibly leukotriene biosynthesis by pulmonary endothelial cells.